1. Field of the Invention
The present invention relates to a magnetic recording medium and a process for the production thereof. More particularly, it is concerned with a magnetic recording medium of the kind which has a thin solid film prepared by the vacuum evaporation of a ferromagnetic material, which film has improved surface strength and slip characteristics.
2. Description of the Prior Art
As for magnetic recording media, those media which are produced by a coating process, in which fine powders of magnetic materials, such as .gamma.-Fe.sub.2 O.sub.3, .gamma.-Fe.sub.2 O.sub.3 doped with Co, Fe.sub.3 O.sub.4, CrO.sub.2, ferromagnetic alloys, etc., are dispersed into organic binders, such as vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, epoxy resin, polyurethane resin, etc., the resulting dispersion are coated on non-magnetic supports and then dried, have been predominantly used. As there has been a growing demand for high density recording in recent years, much attention has been directed to thin solid films of ferromagnetic metals which are formed using a sputtering technique, a vacuum evaporation technique, an ion plating technique or the like, since these techniques have the capability of being used in producing the so-called binder-free magnetic recording medium. Various attempts have, therefore, been undertaken with the intent of using such films practically. However, these magnetic recording media, in which ferrormagnetic thin solid films are only formed on non-magnetic supports, suffer from the disadvantage that the magnetic layers thereof are peeled off or scratched through contact with a recording head during scanning, which differs from magnetic recording media produced by the coating process.
To remove the above-described disadvantage from such recording media, Japanese Patent Application (OPI) No. 12304/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a process wherein the surfaces of binder-free magnetic recording media are covered with macromolecular materials using a coating technique. In addition, Japanese Patent Application (OPI) No. 88704/78 describes a process wherein surface active agents having HLB values of 5 to 30 are provided on the surfaces of binder-free magnetic recording media by coating. In these wet processes, solvents must be used, a fear of environment pollution exists and further, an additional equipment to prevent explosions is required. Moreover, problems arise because oxidation of the surfaces of the ferromagnetic thin solid films due to contact with air occurs, which causes a deterioration thereof, and the number of pinholes made in the ferromagnetic thin solid films with the chance of friction are unavoidable when the ferromagnetic thin solid films are removed from the vacuum system at the conclusion of the evaporation and optionally, must be handled to coat macromolecular materials or surface active agents thereon. The magnetic recording media prepared by the above-described processes become valueless.
Furthermore, Japanese Patent Application (OPI) No. 28844/75 describes both a process in which a ferromagnetic material and a polymer are deposited at the same time using the vapor deposition technique and a process in which a ferromagnetic material and a monomer or an oligomer are deposited at the same time using the vapor deposition technique and subsequently, a polymerization reaction is carried out in the resulting deposited layer. Although these processes are excellent for producing high density recording media, they suffer a serious disadvantage that sufficiently high surface strength cannot be attained because of the insufficiency of the slip characteristics of the deposited layer.